Abstract: Device for filtering a liquid. The filter device is provided with at least two filter elements (8, 15) placed parallel to each other. A three-way cock (6, 13) is accommodated in the pipe (4, 5) to each filter element (8, 15) for connection of the inflow opening of each filter element (8, 15) to a mains system (3) for supplying the liquid with sufficient pressure to press the liquid through the filter device. The three-way cocks (6, 13) are mutually connected by a pipe (19). A drain (23) to a sewer is provided which has a closing device (21), which is connected to a branch point (26) of the pipe (19) via a pipe (20). A three-way cock (10, 17) is accommodated in the pipe (9, 16) of each filter element (8, 15) for connecting the outflow opening of each filter element (8, 15) to a mains system (12) of a user. The three-way taps (10, 17) are mutually connected by a pipe (24).